1. Field of the Invention
The present invention relates to the field of magnetic resonance imaging and more specifically to the field of imaging flowing fluids with magnetic resonance within a subject.
2. Description of Related Art
In magnetic resonance (MR) imaging of a subject, complex fluid flow within, particularly those which vary with time, is the source of artifacts. Methods of minimizing these artifacts include the use of cardiac gating, flow-compensated gradient waveforms and short MR echo times. These methods extract a coherent signal from the acquired MR signals, discarding non-coherent MR signals. Nevertheless, the non-coherent portion of the signal contains useful diagnostic information.
The physiological processes which result in non-coherent MR signals are of great interest clinically, but are very difficult to measure non-invasively. Complex fluid flow, such as turbulence, has been observed in the descending aortas of dogs using hot-film anemometer methods in which upstream blood is heated and its passage observed downstream. This method requires the placement of two catheters, and consequently is highly invasive. It has only been performed in humans undergoing diagnostic X-ray angiographic procedures. The angiography studies suggest that some level of turbulence is present in almost all individuals over the age of forty, and the degree of turbulence increases with both age and the stiffness of the arterial system.
Aside from its invasive nature, another limitation of the hot-film technique is that no imaging information is obtained, since the catheters are point source detectors and their exact radial placement in the vessel is not usually well known.
Currently, there is a need to measure complex fluid flow by non-invasive methods.